The invention relates to an adjusting device for a disc brake and, in particular, to an adjusting device for a pneumatically actuated disc brake.
There are various embodiments of adjusting devices for disc brakes. Thus, for example, there are adjusting devices for pneumatically actuated disc brakes, especially those designed with sliding calipers, and also for pneumatically actuated fixed- or hinged-caliper disc brakes.
Pneumatically actuated disc brakes are now part of the standard equipment of heavy commercial vehicles. To produce the required application force, disc brakes of this kind require mechanical multiplication since the force of the pneumatically operated brake cylinders is limited owing to the pressure level (currently about 10 bar) and the limited size of the brake cylinders. In the case of currently known pneumatically actuated disc brakes, there are multiplication ratios of between 10:1 and 20:1. The piston strokes of the brake cylinders are between 50 and 75 mm, giving an application travel of about 4 mm for pressing the brake pads against the brake disc.
The thickness of the friction material of the brake pads is in a range of 20 mm. Since two pads are required, this results in a wear-related travel of about 40 mm, without taking into account disc wear. This travel is many times greater than the application travel mentioned above. There is therefore a need to adjust the brake according to pad wear by means of a device. The prior art is an automatic wear adjuster, the effect achieved being that the “release clearance”, i.e. the gap between the brake pads and the brake disc in the unactuated state, is held constant irrespective of the state of wear and wear behavior of the brake pads.
Disc brakes that have an adjuster are very often found in commercial vehicles, such adjusters being disposed concentrically in the cavity of a threaded spindle and being driven eccentrically by way of a drive element (e.g. operating finger, gearwheel) by the brake lever.
A known adjusting device 1 of this type is illustrated in FIG. 4. It consists essentially of the following functional elements: shaft 2 with drive spigot 19 for a resetting tool; bearing washer 3 for fixing on a disc brake; compression spring 4 between bearing washer 3 and operating fork 5; operating fork 5 with drive ring 6; load-changeable/overload clutch 8; clutch sleeve 12; and spring 15.
During a braking operation, the brake lever coupled to the piston rod of the brake cylinder performs a rotary motion. Before the rotary motion of the lever is introduced into the adjusting device 1 by way of the coupling mechanism of the adjuster (e.g. operating fork 5 and operating finger or gearwheels), an “idle travel” has to be overcome. This travel is decisive for the size of the release clearance since the adjuster is not activated during this movement, and the application travel thus represents the release clearance. Once this idle travel has been overcome, the adjusting device 1 is set in rotary motion, and an adjusting process is initiated by virtue of the coupling with the threaded spindle or tube via the clutch sleeve 12.
One important element of the adjusting device 1 is the “clutch sleeve” 12. As described above, this is used to transmit the rotary motion of the adjusting device 1 to the “threaded spindle or tube.” In the existing adjusting device 1 in accordance with FIG. 4, this clutch sleeve 12 is embodied integrally with a sleeve body 13. It has two essential functional sections: at one end, the clutch sleeve 12 has a clutch section 10 with pockets to accommodate balls 11 which, together with a clutch bushing 9, form the load-changeable/overload clutch 8 in the form of a “ball ramp clutch”.
The end remote from the clutch sleeve 12 has ribs 14 extending in the axial direction, which are used to transmit the torque to the threaded tube. In the cavity of the clutch sleeve 12 is a spring 15, in particular a cylindrical spring, which is used to preload the ball ramp clutch 8. The cylindrical spring can be supported on a profiled washer 16, which is held by a lip of the shaft 2, and on the clutch section 10. Owing to installation space conditions, the clutch sleeve 12 must be embodied with relatively thin walls. On the other hand, the clutch section 10 must have a greater wall thickness at the end in the region of the ball ramp pockets in order to ensure that the ball pockets have sufficient strength.
Experience has shown that this component is relatively difficult to produce and that the fatigue strength of this component can be impaired in the event of small deviations in the process. As part of higher requirements as regards economy of manufacture and quality (maintenance intervals) in combination with minimum possible installation space and increased strength, there is a requirement for an improved adjusting device.
It is therefore the object of the present invention to provide an improved adjusting device.
This and other objects are achieved by an adjusting device, as well as a disc brake having such an adjusting device, for compensating wear of the brake pads and brake disc of a pneumatically actuated disc brake having a rotary lever-actuated application device, which adjusting device can preferably be inserted into an actuating spindle of the disc brake and attached to a brake caliper of the disc brake by way of a bearing washer, wherein a drive ring is disposed axially on a bushing of a load-changeable/overload clutch. The load-changeable/overload clutch is disposed axially between the drive ring and a clutch sleeve for a spring. The clutch sleeve has a sleeve and a clutch insert that can be inserted axially into the sleeve in a positively engaged manner.
In accordance therewith, such an adjusting device makes it possible significantly to simplify the production of the clutch sleeve and considerably to reduce the sensitivity thereof to process fluctuations.
By virtue of the fact that the clutch sleeve is constructed from two functional components, namely a sleeve and a clutch insert, these two components can be produced by using the most economical methods and with the best-quality results for each component. The clutch insert can be inserted in a simple manner into the sleeve, and it can be connected to the latter in a positively engaged and non-rotatable manner by way of suitable corresponding profiles.
This design has the following advantages:
(1) use of optimum production methods for the decoupled functional components: sintering or cold extrusion for the clutch insert and sheet metal forming for the sleeve, for example;
(2) improved economy over the prior art through a wider choice of suppliers and optimized production processes; and
(3) increased robustness through the use of appropriate manufacturing methods for each of the two different components.
In a preferred embodiment, the load-changeable/overload clutch is designed as a ball ramp clutch with balls, and the balls can be accommodated in ball pockets at one end of the insertable clutch insert. By virtue of the functional decoupling, the clutch insert for the balls is thus easier to fashion than is the case in the prior art.
Provision is furthermore made for the clutch sleeve to have a thrust washer for the spring. To achieve this, it is advantageous if the internal profile of the sleeve forms an axial retainer for the thrust washer.
Various methods are possible for the production of the sleeve, e.g. a drawing process. In a preferred embodiment, the sleeve is designed as a rolled punched/bent part with a joint in the longitudinal direction. The joint can be a weld or positive-locking teeth, for example, but other embodiments are likewise possible.
A disc brake, in particular a pneumatically actuated disc brake, has an adjusting device in accordance with the above description.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.